usb: typec: tps6598x: handle block reads separately with plain-I2C adapters

Quoted 58 lines · Heikki Krogerus

Quoted 56 lines · Guenter Roeck

Quoted 41 lines · Heikki Krogerus

If the I2C adapter that the PD controller is attached to does not support SMBus protocol, the driver needs to handle block reads separately. The first byte returned in block read protocol will show the total number of bytes. It needs to be stripped away.

This is handled separately in the driver only because right now we have no way of requesting the used protocol with regmap-i2c. This is in practice a workaround for what is really a problem in regmap-i2c. The other option would have been to register custom regmap, or not use regmap at all, however, since the solution is very simple, I choose to use it in this case for convenience. It is easy to remove once we figure out how to handle this kind of cases in regmap-i2c.

Fixes 0a4c005bd171 ("usb: typec: driver for TI TPS6598x USB Power Delivery controllers")

Signed-off-by Heikki Krogerus <[email protected]>

---
 drivers/usb/typec/tps6598x.c | 42 ++++++++++++++++++++++++++++++------
 1 file changed, 35 insertions(+), 7 deletions(-)

drivers/usb/typec/tps6598x.c +4 -0

index 8b8406867c02..82f09cd9792d 100644
@@ -73,6 +73,7 @@ struct tps6598x {
 	struct device *dev;
 	struct regmap *regmap;
 	struct mutex lock; /* device lock */
+	u8 i2c_protocol:1;
 
 	struct typec_port *port;
 	struct typec_partner *partner;

@@ -80,6 +81,23 @@ struct tps6598x {
 	struct typec_capability typec_cap;
 };
 
+static int
+tps6598x_block_read(struct tps6598x *tps, u8 reg, void *val, ssize_t len)
+{

drivers/usb/typec/tps6598x.c struct tps6598x { · line 96

Quoted 10 lines

drivers/usb/typec/tps6598x.c +10 -0

+	u8 data[len + 1];
+	int ret;
+
+	if (!tps->i2c_protocol)
+		return regmap_raw_read(tps->regmap, reg, val, len);
+
+	ret = regmap_raw_read(tps->regmap, reg, data, sizeof(data));
+	if (ret)
+		return ret;
+

Sanity check ?

	if (data[0] != len)
		return -Esomething;

Quoted 4 lines

No. Then we would not even need the len parameter. The idea is to allow reading a number of bytes specified by caller, regardless of the maximum size of the block.

If I2C_FUNC_I2C is not supported but I2C_FUNC_SMBUS_I2C_BLOCK is, the regmap core will use i2c_smbus_read_i2c_block_data() and validate the return length. It will return -EIO if it does not match. That seems inconsistent.

Also, I am not sure how you know that at least the minimum required number of bytes is returned if the number of bytes requested is larger than the number of bytes returned by the chip. Am I missing something ?

Also, I notice that your patch does not touch tps6598x_read16(). Yet, according to "TPS65981, TPS65982, and TPS65986 Host Interface Technical Reference Manual", it appears that the 2-byte command used (0x3f) does support/use block commands. Is that an oversight or on purpose ?